Book contents
- Frontmatter
- Contents
- List of Figures
- List of Tables
- Acknowledgements
- A note to the reader
- Part I Organization of the cranial nerves
- 1 General considerations
- 2 Cranial nerve motor fibres and nuclei
- 3 Cranial nerve motor pathways: upper and lower motor neurons
- 4 Cranial nerve sensory fibres, brain stem sensory nuclei and tracts
- Part II-V Individual cranial nerves and functional considerations
- Part II Trigeminal, facial and hypoglossal nerves
- Part III Glossopharyngeal, vagus and accessory nerves
- Part IV Autonomic components of cranial nerves, taste and smell
- Part V Vision, eye movements, hearing and balance: optic, oculomotor, trochlear, abducens and vestibulocochlear nerves
- Further reading
- Index
3 - Cranial nerve motor pathways: upper and lower motor neurons
Published online by Cambridge University Press: 25 August 2009
- Frontmatter
- Contents
- List of Figures
- List of Tables
- Acknowledgements
- A note to the reader
- Part I Organization of the cranial nerves
- 1 General considerations
- 2 Cranial nerve motor fibres and nuclei
- 3 Cranial nerve motor pathways: upper and lower motor neurons
- 4 Cranial nerve sensory fibres, brain stem sensory nuclei and tracts
- Part II-V Individual cranial nerves and functional considerations
- Part II Trigeminal, facial and hypoglossal nerves
- Part III Glossopharyngeal, vagus and accessory nerves
- Part IV Autonomic components of cranial nerves, taste and smell
- Part V Vision, eye movements, hearing and balance: optic, oculomotor, trochlear, abducens and vestibulocochlear nerves
- Further reading
- Index
Summary
Upper and lower motor neurons
Both somatic motor and branchiomotor nerves supply voluntary muscles. Pathways between motor cortex and muscles may be thought of as being arranged in two neuronal groups: upper motor neurons and lower motor neurons. Axons of upper motor neurons decussate before synapsing with lower motor neurons, so the right motor cortex controls the left side of the body, and vice versa – contralateral control.
Upper motor neurons: cortex to nucleus
For cranial nerves, cell bodies of upper motor neurons are in the head and neck area of the motor cortex. Axons descend, decussating just before synapsing with cell bodies of lower motor neurons which make up the motor nucleus of that cranial nerve. The term upper motor neurons is also used clinically to include fibres from other brain centres (e.g. parietal lobe, basal ganglia, cerebellum, reticular formation, midbrain, etc.) that connect with the lower motor neurons in the cranial nerve nucleus, thus influencing their activity.
Lower motor neurons: nucleus to muscle
Cell bodies of lower motor neurons form the brain stem nucleus. Axons leave the brain stem and pass in the cranial nerve to the destination. Thus, although most of the axon of the lower motor neuron is part of the peripheral nervous system, the cell body and first part of the axon is in the central nervous system.
Corticonuclear and corticobulbar
These terms describe the upper motor neuron pathways described above.
- Type
- Chapter
- Information
- Cranial NervesFunctional Anatomy, pp. 24 - 30Publisher: Cambridge University PressPrint publication year: 2005